Download Plants and climate Precipitation and Clouds Warm and cold fronts

Plants and climate
• Q: Does the forest make the rain or the rain
make the forest?
• In Roman times, Egypt and the north of Africa
was green and wooded – goats and
deforestation changed the climate
• Forests cool the air, increase the humidity,
increase chance of rain
• How much damage are humans doing by cutting
down large tracts of the Amazon Forest !!
Warm and cold fronts
• Air masses named for their origin (polar, tropical,
equatorial) and moisture content (maritime, continental)
• Sharp boundaries occur between warm & cold air
masses – called fronts
• Warm air always move up higher than cold air
• Warm front – advancing warm air replaces receding
cold air, gentle slope to transition, steady rain
• Cold front – advancing cold air pushes up receding
warm air, steep slope to transition, heavy rain & storms
• Australia weather mostly experiences cold fronts
Precipitation and Clouds
• Adiabatic cooling occurs when moist air rises
• Air becomes saturated, allowing condensation and
precipitation as rain, hail or snow
• Different types of cloud associated with rain, some
contain ice
• High clouds (> 5 km) – eg cirrus, ice crystals
• Middle clouds (2-7 km) – eg altostratus, mostly water
• Low clouds (< 2 km) – eg stratus (rain), nimbostratus
(snow)
• Vertically developed clouds (via convection) – eg
cumulus, cumulonimbus (thunderstorms)
Thunderstorms
• Friction causes build up of charge
• If strong electric field, ionises air which provides
a conducting path for currents – lightning strikes
(flash & thunder)
• In thunderstorms – don’t stand under (isolated)
trees, hold golf clubs!
• Do stay in a car, if outside crouch down with feet
together.
• Note: If your hair starts to stand on end, run!
• Storms - unstable layers of cold over warm air,
strong convection
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Cyclones, hurricanes, typhoons
• Extreme weather systems – low pressure
cells, clockwise rotation in southern
hemisphere (Coriolis force)
• Name for storms is regional: cyclone is
general term (also used in Australia,
Indian Ocean), hurricane (N Atlantic, NE
Pacific) & typhoon (NW Pacific)
• Only found in latitudes 8° - 20°; driven by
pressure differences & Coriolis force
Cyclones (2)
• Cyclones – start over warm oceans, unstable
moist air and strong convection currents, often
triggered by thunderstorms, diameters 200 –
800 km, winds up to 300 km/h, system moves
slowly
• Tornadoes – diameters < 100 km, winds > 500
km/h, fast moving, occur as waterspouts over
oceans
• Cyclones named for ease of communication –
started by an Australian in early 20th century;
originally female names, now both male &
female, birds, flowers etc
Main ideas to take away
• Atmosphere – necessary for life to exist in
comfort
• Water cycle – principal factor influencing the
weather patterns
• Sun – main energy source, from electromagnetic
radiation
• Thermodynamics – underlying physics;
relationships between heat flows and internal
energy (can be measured by temperature)
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